London: A new study has associated sleep apnea severity with increased cancer mortality.The research adds to evidence presented earlier this year highlighting a link between severe sleep apnea and cancer.

Two further studies presented at the ERS Congress, also show evidence suggesting an increase in cancer incidence among sleep apnea patients and an association between the spread of cancer and sleep apnea.

In the first study, over 5,600 patients from 7 different sleep clinics in Spain were analysed to investigate the link between sleep apnea and cancer mortality.

The severity of sleep apnea was then measured, using a hypoxaemia index. This index measures the amount of time during the night that a person suffers from low levels of oxygen in the blood (less than 90 per cent oxygen saturation).

The results showed that people with sleep apnea who spent more than 14 per cent of their sleep with levels of oxygen saturation below 90 percent (usually severe sleep apnea patients) had approximately double the relative risk of death due to cancer (odds ratio 1.94), than people without sleep apnea.

The results showed that this association was even higher in men and younger people. People with sleep apnea can be treated using continuous positive airway pressure (CPAP) therapy, which generates a stream of air to keep the upper airways open during sleep. In the first study, patients who were not using this device consistently had an increased relative risk (odds ratio 2.56) of death from cancer.

"We found a significant increase in the relative risk of dying from cancer in people with sleep apnea. This adds to evidence presented earlier this year that found for the first time a link between cancer and sleep apnea mortality. Our research has only found an association between these disorders but this does not mean that sleep apnea causes cancer," lead author Dr Miguel Angel Martinez-Garcia from La Fe University Hospital in Valencia, Spain, said.

Similar results were also found in the second study which showed an increase in all-type cancer incidence in people with severe sleep apnea. The link was present even when factors such as age, sex, weight and other comorbidities of participants, were controlled for.

"Further studies are necessary to corroborate our results and analyse the role of CPAP treatment on this association. We hope the findings of our studies will encourage people to get their sleep apnea diagnosed and treated early to help maintain a good quality of life," lead author Dr Francisco Campos-Rodriguez from Valme University Hospital in Seville Spain said.

In a third study, researchers used a mouse model of skin cancer (melanoma) to investigate tumour spread (metastasis) and whether this was associated with sleep apnea.

The results showed that the spread of cancer was more abundant in mice that had been subjected to intermittent hypoxic air, with low levels of oxygen as in sleep apnea, than those who breathed normal air during the experiment.

"The data from this study in animals strongly suggests a link between the spread of cancer and sleep apnea. This provides strong evidence to encourage further study in this area to understand in more detail the links between sleep apneoa and cancer," lead author Professor Ramon Farre from University of Barcelona in Spain said.

The findings have been presented at the European Respiratory Society's (ERS) Annual Congress in Vienna.